Three-dimensional structural body composed of silicon fine wire, its manufacturing method, and device using same

ABSTRACT

A three-dimensional structure composed of highly-reliable silicon ultrafine wires, a method for producing the three-dimensional structure, and a device including the same are provided. The three-dimensional structure composed of silicon fine wires includes wires ( 2 ) on the order of nanometers to micrometers formed by wet etching utilizing the crystallinity of a single-crystal material.

TECHNICAL FIELD

The present invention relates to a three-dimensional structure composedof silicon fine wires. In particular, the present invention relates to athree-dimensional structure using wires on the order of nanometers(referred to as nano) to micrometers formed by etching utilizing thecrystallinity of silicon etc. as elements, a method for producing thesame, and a device including the same.

BACKGROUND ART

Conventionally, a plate or block structure composed of silicon or astructure formed by bending a metal conducting wire provides elementssuch as oscillators and coils.

In general, a tip magnetized with cobalt or iron etc. is used as a tipof an atomic force microscope to detect a magnetic field.

Furthermore, the present inventors have already proposed elements suchas a cantilever composed of a fine three-dimensional structure in thefollowing Patent Document 1 etc.

[Patent Document 1]

Japanese Unexamined Patent Application Publication No. 2001-91441 (pp.7-8, FIG. 4)

[Patent Document 2]

Japanese Unexamined Patent Application Publication No. 2001-289768 (pp.3-4, FIG. 1)

[Patent Document 3]

Japanese Unexamined Patent Application Publication No. 2003-114182 (pp.5-6, FIG. 1)

DISCLOSURE OF INVENTION

However, with the known fine tip described above, in-process control ofthe magnetic force is impossible.

In a scanning temperature microscope, a loop used as the temperaturesensing element is produced by hand or by nanofabrication piece bypiece. Therefore, confirmation tests and multipoint measurements aredifficult to achieve.

Furthermore, a plate-shaped cantilever used in a known scanning forcemicroscope within a scanning electron microscope causes the followingproblems: When scanning electron microscopy observation is performedperpendicularly to the sample, the cantilever blocks the observationpoint, so that it is difficult to observe the sample, and to identifythe observation point.

It is expected that miniaturization of the cantilever using athree-dimensional structure composed of silicon fine wires will improvethe sensitivity in mass spectrometry and force detection. However, inthis technology, damage such as crystal defects in the vicinity of thesurface significantly affects the Q factor as a mechanical oscillator.Such damage in the vicinity of the surface must be reduced. Inparticular, when the three-dimensional structure composed of siliconfine wires is formed by reactive ion etching (anisotropic etching), thedamage such as crystal defects is increased. Therefore, it is importantto study etching techniques.

In view of the above situation, it is an object of the present inventionto provide a highly-reliable three-dimensional structure composed ofsilicon ultrafine wires, a method for producing the same, and a deviceincluding the same.

In order to achieve the above object, the present invention provides thefollowing:

[1] A three-dimensional structure composed of silicon fine wiresincluding wires on the order of nanometers to micrometers formed by wetetching utilizing the crystallinity of a single-crystal material.

[2] The three-dimensional structure composed of silicon fine wiresaccording to [1] above, being a fine coil composed of a plurality of thewires.

[3] A device including a three-dimensional structure composed of siliconfine wires, wherein a magnetic field is generated or detected with afine coil composed of a plurality of wires on the order of nanometers tomicrometers formed by wet etching utilizing the crystallinity of asingle-crystal material.

[4] A device including a three-dimensional structure composed of siliconfine wires, wherein the temperature in a minute area is measured usingthe temperature-dependent resistance variation of a fine coil composedof a plurality of wires on the order of nanometers to micrometers formedby wet etching utilizing the crystallinity of a single-crystal material.

[5] The device including a three-dimensional structure composed ofsilicon fine wires according to [4] above, wherein the fine coil is usedin visualization of the temperature distribution of planar samples,visualization of the temperature distribution and metabolism ofbiological materials, and mapping of the temperature distribution ofelectronic devices.

[6] A device including a three-dimensional structure composed of siliconfine wires, wherein the interaction or the change in force or mass onthe atomic level is detected utilizing the change in amplitude, phase,or self-excited frequency of an oscillator composed of a plurality ofwires on the order of nanometers to micrometers formed by wet etchingutilizing the crystallinity of a single-crystal material.

[7] A device including a three-dimensional structure composed of siliconfine wires, wherein a sample having a specific particle size is trappedin a network structure composed of a plurality of wires on the order ofnanometers to micrometers formed by wet etching utilizing thecrystallinity of a single-crystal material.

[8] The device including a three-dimensional structure composed ofsilicon fine wires according to [7] above, being a filter to absorb aspecific substance, the filter being formed by modifying the surface ofthe network structure.

[9] The device including a three-dimensional structure composed ofsilicon fine wires according to [7] above, wherein the network structureis an elastic body as a whole so that the structure is elastic.

[10] The device including a three-dimensional structure composed ofsilicon fine wires according to [7] above, wherein the network structureis a three-dimensional optical filter, a grating, or a shielding window.

[11] The device including a three-dimensional structure composed ofsilicon fine wires according to [7] above, wherein the network structureis a resistor having a grid structure, thereby providing an electricalcircuit network.

[12] A device including a three-dimensional structure composed ofsilicon fine wires, wherein the three-dimensional structure composed ofa plurality of wires on the order of nanometers to micrometers formed bywet etching utilizing the crystallinity of a single-crystal material,and a tip or a block formed at an intersection of the wires by the wetetching is used as a probe or a mass to provide the structure withpredetermined vibration characteristics.

[13] A device including a three-dimensional structure composed ofsilicon fine wires, wherein the device includes a microscope tip withwhich an observation portion is readily observed, the tip composed of aplurality of wires on the order of nanometers to micrometers formed bywet etching utilizing the crystallinity of a single-crystal material.

[14] A method for producing a three-dimensional structure composed ofsilicon fine wires, the method including the steps of preparing asilicon-on-insulator (SOI) substrate having a surface composed of the{100} surface of silicon single-crystals thereon; forming a siliconoxide film on a part of an SOI layer of the SOI substrate; forming asilicon nitride film on the silicon oxide film and the a part of the SOIlayer; removing a part of the silicon nitride film to expose the SOIlayer such that elongated shapes are repeatedly arranged so as to beparallel to the <110> direction; removing the exposed SOI layer portionsby wet etching; thermally oxidizing the {111} surface exposed by the wetetching to form a thermally-oxidized film; removing a part of theremaining silicon nitride film and wet etching the newly exposed SOIlayer to form an array of silicon fine wires; and removing a buriedoxide film of the SOI substrate to form silicon fine wires that can beindependently oscillated.

[15] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [14] above, wherein proximal ends of thesilicon fine wires are formed so as to have different shapes on the twolateral sides of each fine wire.

[16] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [14] above, wherein the silicon finewires are processed such that each fine wire has the same length.

[17] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [14] above, wherein the silicon finewires are processed such that each fine wire has different length.

[18] A method for producing a three-dimensional structure composed ofsilicon fine wires, the method including the steps of preparing an SOIsubstrate having a surface composed of the {100} surface of siliconsingle-crystals thereon; forming a silicon nitride film on an SOI layerof the SOI substrate; removing a part of the silicon nitride film toexpose the SOI layer such that elongated shapes are repeatedly arrangedso as to be parallel to the <110> direction; removing the exposed SOIlayer portions by wet etching; thermally oxidizing the {111} surfaceexposed by the wet etching to form a thermally-oxidized film; removing apart of the remaining silicon nitride film and wet etching the newlyexposed SOI layer to form an array of silicon fine wires; and removing aburied oxide film of the SOI substrate to form silicon fine wires thatcan be independently oscillated.

[19] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [18] above, wherein proximal ends of thesilicon fine wires are formed so as to have different shapes on the twolateral sides of each fine wire.

[20] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [18] above, wherein the silicon finewires are processed such that each fine wire has the same length.

[21] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [18] above, wherein the silicon finewires are processed such that each fine wire has different length.

[22] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [14] above, wherein thethree-dimensional structure includes probes.

[23] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [22] above, wherein the probes aresingly-supported beams.

[24] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [23] above, wherein the singly-supportedbeams are cantilevers for an atomic force microscope.

[25] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [22] above, wherein the probes aredoubly-supported beams.

[26] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [18] above, wherein thethree-dimensional structure includes probes.

[27] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [26] above, wherein the probes aresingly-supported beams.

[28] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [27] above, wherein the singly-supportedbeams are cantilevers for an atomic force microscope.

[29] The method for producing a three-dimensional structure composed ofsilicon fine wires according to [26] above, wherein the probes aredoubly-supported beams.

[30] A three-dimensional structure composed of silicon fine wiresproduced by the method for producing a three-dimensional structurecomposed of silicon fine wires according to [14] above.

[31] A three-dimensional structure composed of silicon fine wiresproduced by the method for producing a three-dimensional structurecomposed of silicon fine wires according to [18] above.

In other words, the present invention provides the following features:

(1) A coil can be formed using a plurality of silicon fine wires. Thecoil can be used as a fine coil to generate or detect a magnetic field.

(2) A coil can be formed using a plurality of silicon fine wires. Thetemperature in a minute area can be measured utilizing thetemperature-dependent resistance variation of the coil. The coil canalso be used in visualization of the temperature distribution of planarsamples, visualization of the temperature distribution and metabolism ofbiological materials, and mapping of the temperature distribution ofelectronic devices.

(3) An oscillator can be formed using a plurality of silicon fine wires.The interaction or the change in force or mass on the atomic level canbe detected utilizing the change in amplitude, phase, or self-excitedfrequency of the oscillator.

(4) A network structure can be formed using a plurality of silicon finewires. The network structure can be used to trap a sample having aspecific particle size.

(5) A network structure can be formed using a plurality of silicon finewires. The network structure achieves a filter to absorb a specificsubstance by modifying the surface thereof.

(6) A network structure can be formed using a plurality of silicon finewires to function as an elastic body as a whole. The network structureachieves an elastic body less susceptible to damage.

(7) A network structure can be formed using a plurality of silicon finewires. The network structure achieves a three-dimensional opticalfilter, a grating, and a shielding window.

(8) A network structure can be formed using a plurality of silicon finewires. The network structure forms a resistor having a grid shape toachieve an electrical circuit network.

(9) A structure of up to three-dimensions can be formed using aplurality of silicon fine wires. A tip or a block can be formed at anintersection of the silicon fine wires by wet etching. The tip or theblock can be used as a probe or a mass, thereby providing a structurehaving predetermined vibration characteristics.

(10) Singly-supported beams composed of silicon fine wires are provided,in which the crystallinity of silicon is utilized and no damage such ascrystal defects occurs.

(11) Singly-supported beams in which proximal ends of the fine wiresfunctioning as probes have different shapes on the two lateral sides ofeach fine wire are provided. Such singly-supported beams can be producedinexpensively by a simple process that omits a step of forming a siliconoxide film. The singly-supported beams have a durable structure becausethe proximal ends of the singly-supported beams have an asymmetricalshape.

(12) Singly-supported beams having excellent probe characteristics andthe same length are provided.

(13) Singly-supported beams having excellent probe characteristics and adifferent length are provided.

(14) Doubly-supported beams composed of silicon fine wires are provided,in which the crystallinity of silicon is utilized and no damage such ascrystal defects occurs.

(15) Doubly-supported beams having excellent probe characteristics andthe same length are provided.

(16) Doubly-supported beams having excellent probe characteristics and adifferent length are provided.

(17) A three-dimensional structure having singly-supported beams ordoubly-supported beams composed of silicon fine wires and havingexcellent probe characteristics is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a device having a tip supported by aplurality of fine wires according to an embodiment of the presentinvention.

FIG. 2 is a perspective view of an oscillator (device) having a tipsupported by a plurality of fine wires according to an embodiment of thepresent invention.

FIG. 3 is a perspective view of a fine coil (device) composed of aplurality of fine wires according to an embodiment of the presentinvention.

FIG. 4 is a perspective view of an oscillator (device) having tipssupported by two doubly-supported fine wires according to an embodimentof the present invention.

FIG. 5 is a perspective view of a fine coil (device) having a gridstructure composed of fine wires according to an embodiment of thepresent invention.

FIG. 6, according to an embodiment of the present invention, is aperspective view of an oscillator (device) having a tip supported by aplurality of fine wires and used to detect the temperature-dependentresistance variation.

FIG. 7 is a drawing showing a resistance bridge in FIG. 6.

FIG. 8 is a schematic view of a fine coil (device) to which a modulationfunction can be added, according to an embodiment of the presentinvention.

FIG. 9 shows cantilevers functioning as probes composed of silicon finewires according to an embodiment of the present invention.

FIG. 10 shows a production process (No. 1) of the cantilevers(singly-supported beams composed of fine wires) shown in FIG. 9.

FIG. 11 shows a production process (No. 2) of the cantilevers(singly-supported beams composed of fine wires) shown in FIG. 9.

FIG. 12 shows a production process (No. 3) of the cantilevers(singly-supported beams composed of fine wires) shown in FIG. 9.

FIG. 13 shows a production process (No. 4) of the cantilevers(singly-supported beams composed of fine wires) shown in FIG. 9.

FIG. 14 shows a production process (No. 5) of the cantilevers(singly-supported beams composed of fine wires) shown in FIG. 9.

FIG. 15 shows cantilevers functioning as probes composed of silicon finewires according to a first modification of the embodiment of the presentinvention.

FIG. 16 shows cantilevers functioning as probes composed of silicon finewires according to a second modification of the embodiment of thepresent invention.

FIG. 17 shows cantilevers functioning as probes composed of silicon finewires according to an embodiment of the present invention.

FIG. 18 shows a production process (No. 1) of the cantileversfunctioning as probes composed of silicon fine wires shown in FIG. 17.

FIG. 19 shows a production process (No. 2) of the cantileversfunctioning as probes composed of silicon fine wires shown in FIG. 17.

FIG. 20 shows a production process (No. 3) of the cantileversfunctioning as probes composed of silicon fine wires shown in FIG. 17.

FIG. 21 shows cantilevers functioning as probes composed of silicon finewires according to a modification of the embodiment of the presentinvention.

FIG. 22 shows doubly-supported beams functioning as probes composed ofsilicon fine wires according to an embodiment of the present invention.

FIG. 23 shows a production process (No. 1) of the doubly-supported beamsfunctioning as probes composed of silicon fine wires shown in FIG. 22.

FIG. 24 shows a production process (No. 2) of the doubly-supported beamsfunctioning as probes composed of silicon fine wires shown in FIG. 22.

FIG. 25 shows a production process (No. 3) of the doubly-supported beamsfunctioning as probes composed of silicon fine wires shown in FIG. 22.

FIG. 26 shows a production process (No. 4) of the doubly-supported beamsfunctioning as probes composed of silicon fine wires shown in FIG. 22.

FIG. 27 shows doubly-supported beams of fine wires functioning as probescomposed of silicon fine wires according to a modification of theembodiment of the present invention.

FIG. 28 shows doubly-supported beams (wherein proximal ends of the finewires have different shapes on the two lateral sides of each fine wire)functioning as probes composed of silicon fine wires according to anembodiment of the present invention.

FIG. 29 shows a production process (No. 1) of the doubly-supported beams(wherein the proximal ends of the fine wires have different shapes onthe two lateral sides of each fine wire) as functioning probes composedof silicon fine wires shown in FIG. 28.

FIG. 30 shows a production process (No. 2) of the doubly-supported beams(wherein the proximal ends of the fine wires have different shapes onthe two lateral sides of each fine wire) as functioning probes composedof silicon fine wires shown in FIG. 28.

FIG. 31 shows a production process (No. 3) of the doubly-supported beams(wherein the proximal ends of the fine wires have different shapes onthe two lateral sides of each fine wire) as functioning probes composedof silicon fine wires shown in FIG. 28.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described withreference to the drawings.

FIG. 1 is a schematic view of a device having a tip supported by aplurality of fine wires according to an embodiment of the presentinvention.

In this figure, reference numeral 1 indicates a cantilever base,reference numeral 2 indicates a plurality of fine wires, referencenumeral 3 indicates a tip, and reference numeral 4 indicates a sample.

As shown in the figure, since the tip 3 is supported by a plurality offine wires [on the order of nanometers (hereinafter abbreviated as nano)to micrometers], the observation portion of the sample 4 is not blocked.As a result, the portion being observed with the tip 3 can be readilyobserved with an optical microscope or a scanning microscope.

The present inventors have already proposed a fine mechanical oscillatorformed using a semiconductor material, a method for producing the same,and a measuring device including the same in the above-cited PatentDocument 1.

FIG. 2 is a perspective view of an oscillator (device) having a tipsupported by a plurality of fine wires according to an embodiment of thepresent invention.

In this figure, reference numeral 100 indicates an oscillator base,reference numerals 101 and 102 indicate two fine wires, and referencenumeral 103 indicates a tip formed at the intersection of the two finewires 101 and 102.

FIG. 3 is a perspective view of a fine coil (device) composed of aplurality of fine wires according to an embodiment of the presentinvention.

In this figure, reference numeral 200 indicates a fine coil base, andreference numeral 201 indicates a fine coil composed of V-shaped finewires.

FIG. 4 is a perspective view of an oscillator (device) having tipssupported by two doubly-supported fine wires according to an embodimentof the present invention.

In this figure, reference numeral 300 indicates oscillator basesdisposed at both sides, reference numerals 301 and 302 indicate two finewires extending from the oscillator bases 300 disposed at both sidesthereof, respectively, and reference numeral 303 indicates tips formedat the intersection of the two fine wires 301 and 302.

Alternatively, double coils composed of the two doubly-supported finewires may be formed without forming the tips 303 shown in FIG. 4.

FIG. 5 is a perspective view of a fine coil (device) having a gridstructure composed of fine wires according to an embodiment of thepresent invention.

In this figure, reference numeral 400 indicates a fine coil base, andreference numeral 401 indicates a fine coil having a grid structurecomposed of fine wires. This device can also be formed inthree-dimensional structure.

FIG. 6, according to an embodiment of the present invention, is aperspective view of an oscillator (device) having a tip supported by aplurality of fine wires and used to detect the temperature-dependentresistance variation. FIG. 7 is a drawing showing a resistance bridgethereof.

In this figure, reference numeral 500 indicates a cantilever support,reference numeral 501 indicates a plurality of fine wires, and referencenumeral 502 indicates a tip.

In this embodiment, each of the cantilevers composed of the fine wires501 is doped with boron to provide electrical conductivity. In addition,the resistance bridge shown in FIG. 7 is formed at the cantileversupport 500. As a result, the resistance variation due to thetemperature of the cantilever can be detected. Because of thesignificantly low heat capacity, this device can provide highsensitivity and response frequency. In FIG. 7, symbol r₁ represents theresistance of a plurality of the fine wire portions, and symbol r₂ andsymbol r₃ represent the resistances of the cantilever support 500.

According to a method for producing the above devices shown in FIGS. 2to 6, for example, single-crystal silicon is etched with potassiumhydroxide (KOH) to provide a fine wire composed of a plurality ofcrystal faces. An example of such a fine wire is composed of two silicon{111} surfaces and a silicon {100} surface.

Silicon single-crystals have the {111} surface and its equivalentsurfaces disposed in two or more directions. Therefore, depending on thecombination of the crystal faces, a fine wire having different axialdirections can be produced by etching the single-crystal silicon.

Furthermore, depending on the combination of fine wires having differentorientations and fine wires parallel to each other, a one-dimensionalline and various two or three-dimensional structures, such as a coilstructure, a grid structure, a network structure, and an oscillatorstructure, can be achieved. Such a three-dimensional structure isproduced using a multilayered structure composed of, for example,silicon and silicon oxide by masking appropriate areas according towhether the areas are to be etched or not.

The structures produced by the present invention can be used as a beam,a V-shaped coil, a V-shaped resistor, a grid structure, and athree-dimensionally linked structure. In any case, in known methods,these structures are made by hand or by combining plate-shapedcomponents. In contrast, the present invention provides the followingadvantages: The structure can be miniaturized, a plurality of thestructures can be produced at the same time, the structure can beproduced with high uniformity, the structure can be producedthree-dimensionally, the frequency of the structure can be increased,and oscillation loss of the structure can be decreased.

The above beam can be used as a stylus, a singly-supported beam, or aprobe. The V-shaped coil can be used as a fine coil.

The V-shaped resistor can be used as a probe for temperature mapping ina minute area by utilizing the temperature-dependent resistancevariation.

The grid structure can be used as a physical filter or a physical andchemical filter by modifying the surface thereof. In addition, the gridstructure, which is a kind of sponge structure, can achieve apredetermined elasticity, and functions as a filter that selects lightdepending on the direction or the wavelength. Furthermore, when thestructure is vibrated, the structure functions as an optical modulationelement. The absorption of a specific substance can be detected as achange in vibration characteristics of the structure by combining thefilter function of the specific substance with the oscillator function.

In the structure composed of fine wires, the inside of the fine wires isused as a waveguide for light or a waveguide for oscillation, therebycontrolling the propagation of the light or the oscillation.

As described above, fine wires on the order of nano to micrometers canbe achieved by wet etching utilizing the crystallinity of silicon etc.,and a three-dimensional structure using the fine wires as elements canbe achieved. This technology allows elements such as an oscillator, anet, a coil, a heat-generating loop, a filter, and a magnetic sensor onthe order of microns to submicrons to be produced.

As a result, the oscillator can detect force or mass, the net can trap asample having a specific particle size, the coil can generate a finemagnetic field or can detect such a magnetic field, and theheat-generating loop can measure the temperature distribution of asample.

This method is applicable to mass production of a three-dimensionalstructure composed of millions to hundreds of millions of fine wires.

FIG. 8 is a schematic view of a fine coil (device) to which a modulationfunction can be added, according to an embodiment of the presentinvention.

In this figure, reference numeral 600 indicates a fine coil support,reference numeral 601 indicates a fine coil composed of fine wires, andreference numeral 602 indicates a sample.

In this embodiment, when current flows in the fine coil 601 composed offine wires, the fine coil 601 can detect the Lorentz force or itsgradient due to the magnetic field of the sample 602 as a force appliedin the oscillation direction.

This device allows a magnetic profile to be measured without using thecharacteristics of a magnetic tip. Furthermore, a modulation functionsuch as modulation of the current, which cannot be added to knownmagnetic tips, can be added to this device.

The present invention is applicable to a scanning probe microscope,oscillation measurement, analysis of characteristics of surfaces andinterfaces, an electric circuit, a mass detector, an electrical circuitnetwork, a substance-trapping filter, and an elastic material. Thepresent invention is also applicable to the measurements of temperature,the temperature distribution of electronic devices, and the temperaturedistribution and metabolism of biological materials.

In the following aspect of the present invention, the wording “acantilever” generally represents a cantilever used in an atomic forcemicroscope, and the wording “a probe” represents a probe which is notlimited to the cantilever used in the atomic force microscope, butrepresents an element used for various applications such as massdetection and magnetic field detection.

FIG. 9 shows cantilevers functioning as probes composed of silicon finewires according to an embodiment of the present invention. FIG. 9( a) isa perspective view thereof, FIG. 9( b) is a plan view thereof, and FIG.9( c) is a cross-sectional view taken along line L-L in FIG. 9( b).

In this figure, reference numeral 701 indicates a handling wafer,reference numeral 702 indicates a buried oxide film, reference numeral703 indicates a silicon-on-insulator (SOI) layer, and reference numeral707 indicates silicon fine wires (cantilevers composed ofsingly-supported beams), which are formed by utilizing the crystallinityof the SOI layer 703.

A method for producing the cantilevers (singly-supported beams composedof fine wires) will now be described with reference to FIGS. 10 to 14.

(1) FIG. 10( a-1) is a plan view and FIG. 10( a-2) is a perspectiveview. As shown in these figures, in Step S1, the buried oxide film 702is formed on the handling wafer 701, and the SOI layer 703 is formed onthe buried oxide film 702. Herein, arrow A indicates the <100> directionand arrow B indicates the <110> direction.

(2) FIG. 10( b-1) is a plan view and FIG. 10( b-2) is a perspectiveview. As shown in these figures, in Step S2, a silicon oxide (SiO₂) film704 is formed on a part of the SOI layer 703.

(3) FIG. 10( c-1) is a plan view and FIG. 10( c-2) is a perspectiveview. As shown in these figures, in Step S3, a silicon nitride (Si₃N₄)film 705 is deposited thereon.

(4) FIG. 11( d-1) is a plan view, FIG. 11( d-2) is a cross-sectionalview taken along line A-A in FIG. 11( d-1), and FIG. 11( d-3) is across-sectional view taken along line B-B in FIG. 11( d-1). As shown inthese figures, in Step S4, the silicon nitride (Si₃N₄) film 705 ispatterned to form parallel rectangular windows such that an edge 704A ofthe silicon oxide (SiO₂) film 704 appears in each window. The long sidesof each rectangular window are parallel to the <110> direction.

As shown in FIG. 11( d-4), the windows may be opened at one end. Asshown in FIG. 11( d-5), the windows may be opened at both ends. As shownin FIG. 11( d-6), the windows may be opened at the other end.

(5) FIG. 12( e-1) is a plan view, FIG. 12( e-2) is a cross-sectionalview taken along line C-C in FIG. 12( e-1), and FIG. 12( e-3) is across-sectional view taken along line D-D in FIG. 12( e-1). As shown inthese figures, in Step S5, the SOI layer 703 that is exposed in thewindows is subjected to wet etching with an alkaline solution using thesilicon nitride (Si₃N₄) film 705 as the mask, thus forming recessesdefined by <111> surfaces 703A.

(6) FIG. 12( f-1) is a plan view, FIG. 12( f-2) is a cross-sectionalview taken along line E-E in FIG. 12( f-1), and FIG. 12( f-3) is across-sectional view taken along line F-F in FIG. 12( f-1). As shown inthese figures, in Step S6, the resultant wafer is thermally oxidized. Asa result, the exposed <111> surfaces 703A of the silicon are protectedwith a thermally-oxidized film 706.

(7) FIG. 13( g-1) is a plan view, FIG. 13( g-2) is a cross-sectionalview taken along line G-G in FIG. 13( g-1), and FIG. 13( g-3) is across-sectional view taken along line H-H in FIG. 13( g-1). As shown inthese figures, in Step S7, a part of the silicon nitride (Si₃N₄) film705 is removed. Although the figures show a case in which the siliconnitride (Si₃N₄) film 705 partly remains, the entire silicon nitride(Si₃N₄) film 705 may be removed.

(8) FIG. 13( h-1) is a plan view and FIG. 13( h-2) is a cross-sectionalview taken along line I-I in FIG. 13( h-1). As shown in these figures,in Step S8, second wet etching is performed using the thermally-oxidizedfilm 706 as the mask. Consequently, as shown in FIG. 13( h-2), SOIlayers 703′ having a substantially triangular cross-section are formedon the buried oxide film 702, one surface of each SOI layer 703′ beingprotected with the thermally-oxidized film 706.

(9) FIG. 14( i-1) is a plan view and FIG. 14( i-2) is a cross-sectionalview taken along line J-J in FIG. 14( i-1). As shown in these figures,in Step S9, the thermally-oxidized film 706 formed in Step S6, thesilicon nitride (Si₃N₄) film 705 partly left in Step S7, and the siliconoxide (SiO₂) film 704 are removed. As a result, the wire-shaped SOIlayers 703′ having a substantially triangular cross-section are formed.

(10) FIG. 14( j-1) is a plan view and FIG. 14( j-2) is a cross-sectionalview taken along line K-K in FIG. 14( j-1). As shown in these figures,in Step S10, the wire-shaped SOI layers 703′ [cantilevers(singly-supported beams)] having a substantially triangularcross-section are processed to have a predetermined length [for example,by reactive ion etching (RIE)].

(11) Finally, FIG. 14( k-1) is a plan view and FIG. 14( k-2) is across-sectional view taken along line L-L in FIG. 14( k-1). As shown inthese figures, in Step S11, the buried oxide film 702 disposed under thewire-shaped SOI layers 703′ having a substantially triangularcross-section is removed to separate the SOI layers 703′. Thus, siliconfine wires [cantilevers (singly-supported beams)] 707 can be formed fromthe wire-shaped SOI layers 703′ having a substantially triangularcross-section. The silicon fine wires 707 are formed by utilizing thecrystallinity of a single-crystal material, and each of the silicon finewire 707 has the same length.

As described above, the method for producing a three-dimensionalstructure composed of silicon fine wires includes the steps of preparingan SOI substrate having a surface composed of the {100} surface ofsilicon single-crystals thereon; forming a silicon oxide film 704 on apart of an SOI layer 703 of the SOI substrate; forming a silicon nitridefilm 705 on the SOI layer 703 and the silicon oxide film 704; removing apart of the silicon nitride film 705 to expose the SOI layer 703 suchthat elongated shapes are repeatedly arranged side-by-side so as to beparallel to the <110> direction; removing the exposed SOI layer 703 bywet etching with an alkaline solution; thermally oxidizing the {111}surfaces 703A exposed by the wet etching to form a thermally-oxidizedfilm 706; removing a part of the remaining silicon nitride film 705; wetetching the newly exposed SOI layer 703 with an alkaline solution;removing the thermally-oxidized film 706 of the resultant SOI layers703′ having a substantially triangular cross-section, the remainingsilicon nitride film 705, and the silicon oxide film 704; forming anarray of silicon fine wires; processing the silicon fine wires such thatthe silicon fine wires have a predetermined length; and removing aburied oxide film 702 of the SOI substrate to form silicon fine wires[cantilevers (singly-supported beams composed of fine wires)] 707 thatcan be independently oscillated.

FIG. 15 shows cantilevers functioning as probes composed of silicon finewires according to a first modification of the embodiment of the presentinvention. FIG. 15( a) is a perspective view thereof, FIG. 15( b) is aplan view thereof, and FIG. 15( c) is a cross-sectional view taken alongline M-M in FIG. 15( b).

In this embodiment, proximal ends of the silicon fine wires [cantilevers(singly-supported beams composed of fine wires)] 708 are aligned.However, the silicon fine wires 708 are formed such that the length ofeach fine wire gradually changes from one to the next. Other structuresare the same as those of the above silicon fine wires.

FIG. 16 shows cantilevers functioning as probes composed of silicon finewires according to a second modification of the embodiment of thepresent invention. FIG. 16( a) is a perspective view thereof, FIG. 16(b) is a plan view thereof, and FIG. 16( c) is a cross-sectional viewtaken along line N-N in FIG. 16( b).

In this embodiment, distal ends of silicon fine wires [cantilevers(singly-supported beams composed of fine wires)] 709 are formed on thesame line, whereas the proximal ends of the silicon fine wires form aslanted shape. As a result, the length of each fine wire graduallychanges from one to the next. Other structures are the same as those ofthe above silicon fine wires.

As described above, according to the present invention, singly-supportedbeams composed of silicon fine wires that suffer no damage such ascrystal defects can be formed by utilizing the crystallinity of silicon,in contrast to a known example in which cantilevers are formed byanisotropic etching (such as RIE) regardless of the crystallinity ofsilicon.

FIG. 17 shows cantilevers functioning as probes composed of silicon finewires according to an embodiment of the present invention. FIG. 17( a)is a perspective view thereof, FIG. 17( b) is a plan view thereof, andFIG. 17( c) is a cross-sectional view taken along line H-H in FIG. 17(b).

In this figure, reference numeral 801 indicates a handling wafer,reference numeral 802 indicates a buried oxide film, reference numeral803 indicates an SOI layer, and reference numeral 806 indicates siliconfine wires (cantilevers composed of singly-supported beams), which areformed by utilizing the crystallinity of the SOI layer 803.

A method for producing the cantilevers (singly-supported beams in whichproximal ends of the fine wires have different shapes on the two lateralsides of each fine wire) will now be described with reference to FIGS.18 to 20.

(1) FIG. 18( a-1) is a plan view and FIG. 18( a-2) is a perspectiveview. As shown in these figures, in Step S1, the buried oxide film 802is formed on the handling wafer 801, and the SOI layer 803 is formed onthe buried oxide film 802. Herein, arrow A indicates the <100> directionand arrow B indicates the <110> direction.

(2) FIG. 18( b-1) is a plan view and FIG. 18( b-2) is a perspectiveview. As shown in these figures, in Step S2, a silicon nitride (Si₃N₄)film 804 is formed on the SOI layer 803.

(3) FIG. 18( c-1) is a plan view and FIG. 18( c-2) is a cross-sectionalview taken along line A-A in FIG. 18( c-1). As shown in these figures,in Step S3, the silicon nitride (Si₃N₄) film 804 is patterned to formparallel rectangular windows such that the SOI layer 803 appears in eachwindow. The long sides of the rectangular windows are parallel to the<110> direction.

(4) FIG. 18( d-1) is a plan view and FIG. 18( d-2) is a cross-sectionalview taken along line B-B in FIG. 18( d-1). As shown in these figures,in Step S4, wet etching is performed with an alkaline solution using thesilicon nitride (Si₃N₄) film 804 as the mask, thus forming recessesdefined by <111> surfaces 803A.

(5) FIG. 19( e-1) is a plan view and FIG. 19( e-2) is a cross-sectionalview taken along line C-C in FIG. 19( e-1). As shown in these figures,in Step S5, the resultant wafer is thermally oxidized. As a result, theexposed <111> surfaces 803A of the silicon are protected with athermally-oxidized film 805.

(6) FIG. 19( f-1) is a plan view and FIG. 19( f-2) is a cross-sectionalview taken along line D-D in FIG. 19( f-1). As shown in these figures,in Step S6, the silicon nitride (Si₃N₄) film 804 is partly removed suchthat the silicon nitride (Si₃N₄) film 804 remains at both ends of therectangular windows.

(7) FIG. 19( g-1) is a plan view and FIG. 19( g-2) is a cross-sectionalview taken along line E-E in FIG. 19( g-1). As shown in these figures,in Step S7, second wet etching is performed using the thermally-oxidizedfilm 805 as the mask. Consequently, SOI layers 803′ [singly-supportedbeams in which proximal ends of the fine wires functioning as probeshave different shapes on the two lateral sides of each fine wire] havinga substantially triangular cross-section are formed on the buried oxidefilm 802, one surface of each SOI layer 803′ being protected with thethermally-oxidized film 805.

(8) FIG. 20( h-1) is a plan view and FIG. 20( h-2) is a cross-sectionalview taken along line F-F in FIG. 20( h-1). As shown in these figures,in Step S8, the thermally-oxidized film 805 formed in Step S5 and thesilicon nitride (Si₃N₄) film 804 remaining at both ends are removed. Asa result, the wire-shaped SOI layers 803′ [singly-supported beams inwhich the proximal ends of the fine wires have different shapes on thetwo lateral sides of each fine wire] having a substantially triangularcross-section are formed.

(9) FIG. 20( i-1) is a plan view and FIG. 20( i-2) is a cross-sectionalview taken along line G-G in FIG. 20( i-1). As shown in these figures,in Step S9, the wire-shaped SOI layers 803′ having a substantiallytriangular cross-section are processed by, for example, RIE so as tohave a predetermined length.

(10) Finally, FIG. 20( j-1) is a plan view and FIG. 20( j-2) is across-sectional view taken along line H-H in FIG. 20( j-1). As shown inthese figures, in Step S10, the buried oxide film 802 disposed under thewire-shaped SOI layers 803′ having a substantially triangularcross-section is removed. Then, the wire-shaped SOI layers 803′ having asubstantially triangular cross-section are separated from the handlingwafer 801 to form singly-supported beams 806 in which the proximal endsof the fine wires have different shapes on the two lateral sides of eachfine wire.

FIG. 21 shows cantilevers functioning as probes composed of silicon finewires according to a modification of the embodiment of the presentinvention. FIG. 21( a) is a perspective view thereof, FIG. 21( b) is aplan view thereof, and FIG. 21( c) is a cross-sectional view taken alongline I-I in FIG. 21( b).

In this embodiment, proximal ends of silicon fine wires [cantilevers(singly-supported beams composed of fine wires)] 807 have differentshapes on the two lateral sides of each fine wire. Furthermore, thesilicon fine wires [cantilevers (singly-supported beams composed of finewires)] 807 are formed such that the length of each fine wire graduallychanges from one to the next. Other structures are the same as those ofthe above silicon fine wires.

As described above, the singly-supported beams 806 and 807 in which theproximal ends of the fine wires functioning as probes have differentshapes on the two lateral sides of each fine wire can be producedinexpensively by a simple process that omits a step of forming a siliconoxide film. These singly-supported beams have a durable structurebecause the proximal ends of the singly-supported beams have anasymmetrical shape. Accordingly, singly-supported beams havingdurability against aging, not being easily broken, and utilizing thecrystallinity of silicon can be formed.

FIG. 22 shows doubly-supported beams functioning as probes composed ofsilicon fine wires according to an embodiment of the present invention.FIG. 22( a) is a perspective view thereof, FIG. 22( b) is a plan viewthereof, and FIG. 22( c) is a cross-sectional view taken along line K-Kin FIG. 22( b).

In this figure, reference numeral 901 indicates a handling wafer,reference numeral 902 indicates a buried oxide film, reference numeral903 indicates an SOI layer, and reference numeral 907 indicates siliconfine wires (doubly-supported beams), which are formed by utilizing thecrystallinity of the SOI layer 903.

A method for producing the doubly-supported beams composed of fine wireswill now be described with reference to FIGS. 23 to 26.

(1) FIG. 23( a-1) is a plan view and FIG. 23( a-2) is a perspectiveview. As shown in these figures, in Step S1, the buried oxide film 902is formed on the handling wafer 901, and the SOI layer 903 is formed onthe buried oxide film 902. Herein, arrow A indicates the <100> directionand arrow B indicates the <110> direction.

(2) FIG. 23( b-1) is a plan view and FIG. 23( b-2) is a perspectiveview. As shown in these figures, in Step S2, a silicon oxide (SiO₂) film904 is formed by patterning both ends of the SOI layer 903.

(3) FIG. 23( c-1) is a plan view and FIG. 23( c-2) is a perspective viewof FIG. 23( c-1). As shown in these figures, in Step S3, a siliconnitride (Si₃N₄) film 905 is deposited on the entire surface.

(4) FIG. 24( d-1) is a plan view, FIG. 24( d-2) is a cross-sectionalview taken along line A-A in FIG. 24( d-1), and FIG. 24( d-3) is across-sectional view taken along line B-B in FIG. 24( d-1). As shown inthese figures, in Step S4, the silicon nitride (Si₃N₄) film 905 ispatterned to form rectangular windows such that the silicon oxide (SiO₂)film 904 appear in both ends of each window. As shown in FIG. 24( d-4),the shape of the windows may be opened at both ends, or as shown in FIG.24( d-5), the shape of the windows may be opened at only the bottom end.

(5) FIG. 24( e-1) is a plan view, FIG. 24( e-2) is a cross-sectionalview taken along line C-C in FIG. 24( e-1), and FIG. 24( e-3) is across-sectional view taken along line D-D in FIG. 24( e-1). As shown inthese figures, in Step S5, wet etching is performed with an alkalinesolution using the silicon nitride (Si₃N₄) film 905 as the mask, thusforming recesses defined by <111> surfaces 903A.

(6) FIG. 25( f-1) is a plan view, FIG. 25( f-2) is a cross-sectionalview taken along line E-E in FIG. 25( f-1), and FIG. 25( f-3) is across-sectional view taken along line F-F in FIG. 25( f-1). As shown inthese figures, in Step S6, the resultant wafer is thermally oxidizedusing the silicon nitride (Si₃N₄) film 905 as the mask. As a result, theexposed <111> surfaces 903A of the silicon are protected with athermally-oxidized film 906.

(7) FIG. 25( g-1) is a plan view, FIG. 25( g-2) is a cross-sectionalview taken along line G-G in FIG. 25( g-1), and FIG. 25( g-3) is across-sectional view taken along line H-H in FIG. 25( g-1). As shown inthese figures, in Step S7, the silicon nitride (Si₃N₄) film 905 isremoved.

(8) FIG. 26( h-1) is a plan view and FIG. 26( h-2) is a cross-sectionalview taken along line I-I in FIG. 26( h-1). As shown in these figures,in Step S8, second wet etching is performed using the thermally-oxidizedfilm 906 as the mask. Consequently, SOI layers 903′ (doubly-supportedbeams functioning as probes) having a substantially triangularcross-section are formed on the buried oxide film 902, one surface ofeach SOI layer 903′ being protected with the thermally-oxidized film906.

(9) FIG. 26( i-1) is a plan view and FIG. 26( i-2) is a cross-sectionalview taken along line J-J in FIG. 26( i-1). As shown in these figures,in Step S9, the thermally-oxidized film 906 formed in Step S6 isremoved. As a result, the wire-shaped SOI layers 903′ (doubly-supportedbeams functioning as probes) having a substantially triangularcross-section are formed.

(10) FIG. 26( j-1) is a plan view and FIG. 26( j-2) is a cross-sectionalview taken along line K-K in FIG. 26( j-1). As shown in these figures,in Step S10, the buried oxide film 902 disposed under the wire-shapedSOI layers 903′ having a substantially triangular cross-section isremoved. As a result, the wire-shaped SOI layers 903′ having asubstantially triangular cross-section are separated from the handlingwafer 901. Thus, probes 907, i.e., doubly-supported beams, composed ofsilicon fine wires utilizing the crystallinity of the SOI layer 903 areformed.

As described above, the method for producing a three-dimensionalstructure composed of silicon fine wires includes the steps of preparingan SOI substrate having a surface composed of the {100} surface ofsilicon single-crystals thereon; forming a silicon oxide film 904 onboth ends of an SOI layer 903 of the SOI substrate; forming a siliconnitride film 905 on the silicon oxide film 904; removing a part of thesilicon nitride film 905 to expose the SOI layer 903 such that elongatedshapes are repeatedly arranged side-by-side so as to be parallel to the<110> direction; removing the exposed SOI layer 903 by wet etching withan alkaline solution; thermally oxidizing the {111} surfaces 903Aexposed by the wet etching; removing all of the remaining siliconnitride film 905; wet etching the newly exposed SOI layer 903 with analkaline solution; forming an array of silicon fine wires; and removinga buried oxide film 902 of the SOI substrate to form silicon fine wires907 that can be independently oscillated.

FIG. 27 shows doubly-supported beams of fine wires functioning as probescomposed of silicon fine wires according to a modification of theembodiment of the present invention. FIG. 27( a) is a perspective viewthereof, FIG. 27( b) is a plan view thereof, and FIG. 27( c) is across-sectional view taken along line L-L in FIG. 27( b).

In this embodiment, the doubly-supported beams composed of fine wires908 are formed such that the length of each fine wire gradually changesfrom one to the next. Other structures are the same as those of theabove silicon fine wires.

As described above, according to the present invention, doubly-supportedbeams composed of silicon fine wires that suffer no damage such ascrystal defects can be formed by utilizing the crystallinity of silicon,in contrast to a known method in which doubly-supported beams are formedby anisotropic etching (such as RIE) regardless of the crystallinity ofsilicon.

FIG. 28 shows doubly-supported beams (wherein proximal ends of the finewires have different shapes on the two lateral sides of each fine wire)functioning as probes composed of silicon fine wires according to anembodiment of the present invention. FIG. 28( a) is a perspective viewthereof, FIG. 28( b) is a plan view thereof, and FIG. 28( c) is across-sectional view taken along line G-G in FIG. 28( b).

In this figure, reference numeral 1001 indicates a handling wafer,reference numeral 1002 indicates a buried oxide film, reference numeral1003 indicates an SOI layer, and reference numeral 1006 indicatessilicon fine wires (doubly-supported beams) in which the proximal endshave different shapes on the two lateral sides of each fine wire, thesilicon fine wires being formed by utilizing the crystallinity of theSOI layer 1003.

A method for producing the doubly-supported beams composed of fine wireswill now be described with reference to FIGS. 29 to 31.

(1) FIG. 29( a-1) is a plan view and FIG. 29( a-2) is a perspectiveview. As shown in these figures, in Step S1, the buried oxide film 1002is formed on the handling wafer 1001, and the SOI layer 1003 is formedon the buried oxide film 1002. Herein, arrow A indicates the <100>direction and arrow B indicates the <110> direction.

(2) FIG. 29( b-1) is a plan view and FIG. 29( b-2) is a perspectiveview. As shown in these figures, in Step S2, a silicon nitride (Si₃N₄)film 1004 is formed on the entire surface of the SOI layer 1003.

(3) FIG. 29( c-1) is a plan view and FIG. 29( c-2) is a cross-sectionalview taken along line A-A in FIG. 29( c-1). As shown in these figures,in Step S3, the silicon nitride (Si₃N₄) film 1004 is patterned to formrectangular windows.

(4) FIG. 30( d-1) is a plan view and FIG. 30( d-2) is a cross-sectionalview taken along line B-B in FIG. 30( d-1). As shown in these figures,in Step S4, wet etching is performed with an alkaline solution using thesilicon nitride (Si₃N₄) film 1004 as the mask, thus forming recessesdefined by <111> surfaces 1003A.

(5) FIG. 30( e-1) is a plan view and FIG. 30( e-2) is a cross-sectionalview taken along line C-C in FIG. 30( e-1). As shown in these figures,in Step S5, the resultant wafer is thermally oxidized using the siliconnitride (Si₃N₄) film 1004 as the mask. As a result, the exposed <111>surfaces 1003A of the silicon are protected with a thermally-oxidizedfilm 1005.

(6) FIG. 30( f-1) is a plan view and FIG. 30( f-2) is a cross-sectionalview taken along line D-D in FIG. 30( f-1). As shown in these figures,in Step S6, the silicon nitride (Si₃N₄) film 1004 is partly removed suchthat the length of the removed portion is shorter than the length of therectangular windows.

(7) FIG. 31( g-1) is a plan view and FIG. 31( g-2) is a cross-sectionalview taken along line E-E in FIG. 31( g-1). As shown in these figures,in Step S7, second wet etching is performed using the thermally-oxidizedfilm 1004 as the mask. Consequently, SOI layers 1003′ (doubly-supportedbeams functioning as probes) having a substantially triangularcross-section are formed on the buried oxide film 1002, one surface ofeach SOI layer 1003′ being protected with the thermally-oxidized film1005.

(8) FIG. 31( h-1) is a plan view and FIG. 31( h-2) is a cross-sectionalview taken along line F-F in FIG. 31( h-1). As shown in these figures,in Step S8, the thermally-oxidized film 1005 formed in Step S5 and thesilicon nitride (Si₃N₄) film 1004 are removed. As a result, thewire-shaped SOI layers 1003′ (doubly-supported beams) having asubstantially triangular cross-section are formed.

(9) FIG. 31( i-1) is a plan view and FIG. 31( i-2) is a cross-sectionalview taken along line G-G in FIG. 31( i-1). As shown in these figures,in Step S9, the buried oxide film 1002 disposed under the wire-shapedSOI layers 1003′ having a substantially triangular cross-section isremoved. As a result, silicon fine wires (doubly-supported beams) 1006having different shapes on the two lateral sides of each fine wire areformed by utilizing the crystallinity of the SOI layer 1003.

As described above, the silicon fine wires (doubly-supported beams) 1006having different shapes on the two lateral sides of each fine wire canbe produced inexpensively by a simple process that omits a step offorming a silicon oxide film. These doubly-supported beams have adurable structure because the proximal ends of each doubly-supportedbeam have an asymmetrical shape. Accordingly, doubly-supported beamshaving durability against aging, not being easily broken, and utilizingthe crystallinity of silicon can be formed.

The present invention is not limited to the above embodiments. Variousmodifications can be made based on the purpose of the present invention,and those modifications are not excluded from the scope of the presentinvention.

As described above in detail, the present invention provides thefollowing advantages.

(A) An oscillator composed of fine wires can be achieved. As a result,the oscillation direction can be limited depending on the combination ofthe fine wires. In addition, since the fine wires have a smooth crystalface, the oscillation loss due to the surface can be reduced. As aresult, an oscillator having a high Q factor can be achieved.

(B) An oscillator composed of fine wires can be achieved. As a result,an oscillator wherein the decrease in characteristic frequency and thedecrease in the Q factor are low even in a liquid can be achieved.Accordingly, an oscillator suitable for higher sensitivity andhigh-speed detection can be achieved.

(C) An oscillator composed of fine wires can be achieved. The oscillatorcan be used as a coil that can generate a magnetic field or detect amagnetic field as Lorentz force in response to a current flow.

(D) A coil composed of fine fires can be achieved. As a result, the coilcan detect the temperature-dependent resistance variation in the areawhere the coil is in contact with a sample. Thus, the temperature in aminute area of the sample can be measured. As a result, mapping of thetemperature distribution of electronic devices and mapping of thedistribution of the temperature and metabolism of biological materialscan be achieved. Furthermore, since a large number of fine coils can beproduced with high uniformity, confirmation tests and multipointmeasurements can be performed.

(E) A network structure can be formed using a plurality of fine wires,thereby trapping samples having a specific particle size.

(F) A network structure can be formed using a plurality of fine wires.As a result, the network structure can achieve a filter to adsorb aspecific substance by modifying the surface thereof. This filter haschemical and physical selectivity.

(G) A network structure can be formed using a plurality of fine wires tofunction as an elastic body as a whole.

(H) A network structure can be formed using a plurality of fine wires,thereby achieving a three-dimensional optical filter, a grating, and ashielding window. A three-dimensional structure having a regular shapecan be achieved, and therefore, selectivity depending on the directionand the wavelength can be obtained. An optical modulation element can beachieved by vibrating the structure.

(I) A network structure can be formed using a plurality of fine wires.This network structure forms a resistor having a grid shape to achievean electrical circuit network. The electrical circuit network having thenetwork structure can be achieved, thereby realizing a finethree-dimensional body that can perform three-dimensional sensing.

(J) A structure of up to three-dimensions can be formed using aplurality of fine wires. A tip or a block can be formed at anintersection of the fine wires by wet etching. The tip or the block canbe used as a probe or a mass, thereby providing a structure havingpredetermined vibration characteristics. As a result, this structure cancontrol the vibration characteristics, which can normally be controlledonly with a macroscopic structure or a handmade three-dimensionalstructure. Furthermore, this structure provides a high Q factor and highdesign flexibility.

(K) A cantilever composed of fine wires and a tip used in a scanningprobe microscope can be formed. In optical microscopy or scanningelectron microscopy performed perpendicularly with respect to a sample,even the close vicinity of the tip can be directly observed using thiscantilever. As a result, the relationship between the relative positionsof microscope images can be obtained and each microscopy can beperformed more readily.

In other words, the following can be achieved: (1) the generation of amagnetic field and the detection of a magnetic field by realizing a finecoil, and the improvement in detection sensitivity by modulating thecurrent flowing in the coil; (2) temperature measurement and mapping byrealizing a fine resistor; (3) the detection of mass and force on theatomic level by the achievement of a fine oscillator; (4) theachievement of an oscillator having a low oscillation loss and a lowdecease in frequency in liquid by realizing a fine oscillator, and theimprovement of the sensitivity and increase in the frequency thereby;(5) physical and chemical filtering functions by a finethree-dimensional structure; (6) the achievement of an optical elementcomposed of a fine three-dimensional structure; (7) a scanning probemicroscope within an optical microscope or a scanning electronmicroscope wherein the field of view is not easily blocked; and (8) theimprovement of confirmation test reliability and the achievement ofmultipoint measurements as a result of the production, with highuniformity, of a large number of the various structures or sensingelements mentioned above.

(L) In the present invention, singly-supported beams composed of siliconfine wires that suffer no damage such as crystal defects can be formedby utilizing the crystallinity of silicon, in contrast to a known methodin which singly-supported beams are formed by anisotropic etching (suchas RIE) regardless of the crystallinity of silicon.

(M) Singly-supported beams in which proximal ends of the fine wiresfunctioning as probes have different shapes on the two lateral sides ofeach fine wire are provided. Such singly-supported beams can be producedinexpensively by a simple process that omits a step of forming a siliconoxide film. These singly-supported beams have a durable structurebecause the proximal ends of the singly-supported beams have anasymmetrical shape. Accordingly, singly-supported beams havingdurability against aging, not being easily broken, and utilizing thecrystallinity of silicon can be formed.

(N) Singly-supported beams having excellent probe characteristics andthe same length can be readily formed.

(O) Singly-supported beams having excellent probe characteristics anddifferent length can be readily formed.

(P) Doubly-supported beams composed of silicon fine wires that suffer nodamage such as crystal defects can be formed by utilizing thecrystallinity of silicon, in contrast to a known method in whichdoubly-supported beams are formed by anisotropic etching (such as RIE)regardless of the crystallinity of silicon.

(Q) Doubly-supported beams in which the proximal ends of the fine wiresfunctioning as probes have different shapes on the two lateral sides ofeach fine wire are provided. These doubly-supported beams have a durablestructure because the proximal ends of each doubly-supported beam havean asymmetrical shape. Accordingly, doubly-supported beams havingdurability against aging, not being easily broken, and utilizing thecrystallinity of silicon can be formed.

(R) Doubly-supported beams having excellent probe characteristics andthe same length can be readily formed.

(S) Doubly-supported beams having excellent probe characteristics anddifferent length can be readily formed.

(T) A three-dimensional structure including singly-supported beams ordoubly-supported beams composed of silicon fine wires, and havingexcellent probe characteristics can be produced.

INDUSTRIAL APPLICABILITY

The present invention is suitable for reading out very high-densityinformation, measuring mechanical or physical properties of minutesamples, and measuring magnetism or atomic force with high resolution.The present invention is particularly useful as a measurement technologyon the order of nanometers.

1. A method for producing a three-dimensional structure composingsilicon fine wires, the method comprising the steps of: preparing asilicon-on-insulator (SOI) substrate having a surface composed of the{100} surface of silicon single-crystals thereon; forming a siliconoxide film on a part of an SOI layer of the SOI substrate; forming asilicon nitride film on the silicon oxide film and the part of the SOIlayer; removing a part of the silicon nitride film to expose the SOIlayer such that elongated shapes are repeatedly arranged so as to beparallel to the <110> direction; removing the exposed SOI layer portionsby wet etching; thermally oxidizing the {111} surface exposed by the wetetching to form a thermally-oxidized film; removing a part of theremaining silicon nitride film and wet etching the newly exposed SOIlayer to form an array of silicon fine wires; and removing a buriedoxide film of the SOI substrate to form silicon fine wires that can beindependently oscillated, wherein the silicon fine wires are processedsuch that each fine wire has a different length.
 2. A method forproducing a three-dimensional structure composing silicon fine wires,the method comprising the steps of: preparing an SOI substrate having asurface composed of the {100} surface of silicon single-crystalsthereon; forming a silicon nitride film on an SOI layer of the SOIsubstrate; removing a part of the silicon nitride film to expose the SOIlayer such that elongated shapes are repeatedly arranged so as to beparallel to the <110> direction; removing the exposed SOI layer portionsby wet etching; thermally oxidizing the {111} surface exposed by the wetetching to form a thermally-oxidized film; removing a part of theremaining silicon nitride film and wet etching the newly exposed SOIlayer to form an array of silicon fine wires; and removing a buriedoxide film of the SOI substrate to form silicon fine wires that can beindependently oscillated, wherein the silicon fine wires are processedsuch that each fine wire has a different length.
 3. The method forproducing a three-dimensional structure composing silicon fine wiresaccording to claim 1, wherein the three-dimensional structure comprisesprobes.
 4. The method for producing a three-dimensional structurecomposing silicon fine wires according to claim 3, wherein the probesare singly-supported beams.
 5. The method for producing athree-dimensional structure composing silicon fine wires according toclaim 4, wherein the singly-supported beams are cantilevers for anatomic force microscope.
 6. The method for producing a three-dimensionalstructure composing silicon fine wires according to claim 3, wherein theprobes are doubly-supported beams.
 7. The method for producing athree-dimensional structure composing silicon fine wires according toclaim 2, wherein the three-dimensional structure comprises probes. 8.The method for producing a three-dimensional structure composing siliconfine wires according to claim 7, wherein the probes are singly-supportedbeams.
 9. The method for producing a three-dimensional structurecomposing silicon fine wires according to claim 8, wherein thesingly-supported beams are cantilevers for an atomic force microscope.10. The method for producing a three-dimensional structure composingsilicon fine wires according to claim 7, wherein the probes aredoubly-supported beams.
 11. A three-dimensional structure comprisingsilicon fine wires produced by the method for producing athree-dimensional structure composing silicon fine wires according toclaim
 1. 12. A three-dimensional structure comprising silicon fine wiresproduced by the method for producing a three-dimensional structurecomposing silicon fine wires according to claim 2.